Frequency stable coaxial magnetron utilizing low coefficient of thermal expansion material



Aprll 30, 1968 w. A. GERARD 3,381,168

FREQUENCY STABLE COAXIAL MAGNETRON UTILIZING LOW COEFFICIENT OF" THERMAL EXPANSION MATERIAL Filed Dec. 1, 1964 2 Sheets-Sheet (Ill/ll l LOW COEFFICIENT OF THERMAL INVENTOR 2| EXPANS'ON MATERIAL William A. Gerard LOW THERMAL v CONDUCTIVITY BY BUTTONS M ATTORNEY April 30, 1968 w. A. GERARD 3,381,168

FREQUENCY STABLE COAXIAL MAGNETRON UTILIZING LOW COEFFICIENT OP THERMAL EXPANSION MATERIAL Filed Dec. 1, 1964 2 Sheets-Sheet United States Patent 3,381,168 FREQUENCY STABLE COAXIAL MAGNETRON UTILIZING LOW COEFFICIENT 0F THERMAL EXPANSION MATERIAL William A. Gerard, Horseheads, N.Y., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Dec. 1, 1964, Ser. No. 415,073 6 Claims. (Cl. 315--39.75)

ABSTRACT OF THE DISCLOSURE This invention relates to a coaxial magnetron in which the outer cavity resonator is provided with a cylindrical outer wall member of a material having a low coefiicient of thermal expansion. This cylindrical member of low expansion material serves as the outer diameter of the outer cavity resonator and is secured to the main body of the outer cavity resonator by low thermal conductive means. The remaining portion of the outer cavity resonator provides means of transmitting heat from the anode of the magnetron to the exterior.

This invention relates to electron discharge devices and, more particularly, to coaxial magnetron type devices.

In the R. J. Collier et al. Patent 2,854,603 issued Sept. 30, 1958, there is disclosed a coaxial magnetron structure which comprises an inner and outer resonant system. The inner resonant system includes. a cylindrical anode together with a plurality of anode vanes radially extending inwardly therefrom. These vanes define a circumfcrential array of inner, or anode, cavity resonators. An outer cavity resonator is defined between an outer cylindrical wall and the cylindrical anode wall. The two systems are coupled together by a circumferential array of slots through the cylindrical anode wall which connect the outer resonant system with the anode cavity resonators. The inner resonant system is designed to oscillate in the pi mode, while the outer system is designed to oscillate in the TE mode.

Such a structural arrangement overcomes many disadvantages inherent in magnetrons of prior design. In general, the frequency of oscillation of the coaxial magnetron is controlled by the outer resonant cavity to a very high degree. The frequency of the coaxial magrte-tron is thus mainly a function in decreasing order of the outer diameter of the outer cavity, the outer cavity length, the inner diameter of the outer cavity and the length of the anode vanes. If all of these components are made of copper as the critical elements are in conventional magnetrons both tubes would be expected to have a similar coefiicient of thermal expansion. This has been found to be about 2 megacycle per degree centigrade, in a 9.000 mc. (K band) magnetron.

One particular problem associated with magnetrons is the situation wherein there is a momentary loss of air pressure utilized for cooling the magnetron and as a result there may be a sudden rise in temperature of the magnetron. If this should happen, then there will be a sudden frequency shift which is very detrimental to the operation of a radar system employing the magnetron.

Several methods of temperature compensation have been employed in the past. A typical method is to employ a tuner and a length of bimetallic materials. If the cavity expands due to rise in temperature, the bimetallic materials decrease the effective length of a tuning member associated with the cavity. This, in effect, cancels the frequency change due to the expansion of the cavity. This technique is found to have several disadvantages such as requiring an excessive length of tuner mechanism. In addition, the tuner is thermally isolated from the tube and the action is extremely sluggish and may not be effective for five or ten minutes during which time the frequency control may have been completely lost.

It is accordingly an object of this invention to provide an improved electron discharge device.

It is a further object to provide an improved coaxial magnetron.

It is another object to provide an improved temperature compensation system for a coaxial magnetron.

It is another object to provide an improved temperature compensation mechanism for a coaxial magnetron which is capable of preventing frequency shift due to a sudden rise in temperature.

Briefly, the present invention provides a coaxial magnetron having an outer cavity resonator which is provided with a cylinder of low expansion material serving as the outer diameter of the cavity resonator and secured to the main body of the cavity resonator by a semi-rigid joining member of low thermal conductivity.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claimed annexed to and forming a part of the specification.

For a better understanding of the present invention, reference may be had to the accompanying drawings in which:

FIGURE 1 is a perspective view partly in section and partly broken away of a coaxial magnetron embodying the present invention; and

FIG. 2 is a side view in elevation of the device in FIG. 1 in which magnets have been added.

Referring now to the drawings, there is shown a coaxial magnetron embodying the present invention. The magnetron is of the type more fully described in the US. Patent 3,263,118 by H. P. Peasley et al. filed July 30, 1963 and assigned to the same assignee as this present invention. The magnetron is comprised of a body member 10 which is substantially cup-shaped and includes a substantially cylindrical outer wall 12 and a lower end cover 14. The body 10 is of a suitable electrically and thermally conductive material such as copper. Heat radiating fins 13 of a suitable material such as copper are provided on the external portion of the outer side wall 12.

Centrally disposed within the body 10 is a cathode 16 which includes a sleeve member 18 of the suitable material such as molybdenum having thereon an electron emissive coating 20 of a suitable material such as barium oxide. Surrounding the cathode 16 is a substantially cylindrical anode wall 22 having a plurality of anode vanes 24 which extend radially inwardly therefrom. The planes of the anode vanes 24 are inclusive of the axis of the cylindrical anode 22 and they define in cooperation with the anode 22 an array of anode cavity resonators, 26. This array of anode cavity resonators 26 is referred to as the inner cavity resonant system. Coupling slots 28 extend through the cylindrical anode 22 and are centered between adjacent anode vanes 24. The slots 28 communicate with alternate ones of the cavity resonators, 26. The slots 28 extend along the anode wall 22 for a substantial distance, beyond the ends of the anode vanes 24.

A cylindrical member 15 is provided adjacent to the outer side wall 12 and is of a material having a low coefficient of expansion with temperatures such as molybdenum, Invar of the nickel-cobalt-iron alloy sold under the trademark Kovar. The cylindrical member 15 is provided with a copper plating 19 on the inner surface facing the anode 22 to provide a suitable electrically conducting surface. The cylindrical member or liner 15 is physically connected or attached to the main body 10. The member 15 is secured to the outer wall 12 by semi-rigid joining members 17 of a suitable material such as molybdenum and of a low thermal conductivity. In the specific embodiment shown the connecting means 17 are a plurality of small button like members. In the specific embodiment shown, the cylinder 15 extends into a groove 21 in the surface of the lower end plate 14. The cylindrical member 17 and the cylindrical anode 22 along with the lower end plate 14 of the body define in part an outer cavity resonator 30. Extending through the cylindrical wall 15 and the outer wall 12 to provide communication of energy from the output cavity resonator 30 to an external load is an output coupling slot 32. The coupling slot 32 serves as a means by which energy may be removed from the outer cavity resonator 3t and has been shown in its simplest forms for the purpose of simplicity.

Positioned atop the cup-shaped cavity is a substantial disc shaped cover means 34. The cover 34 is of a suitable non-magnetic material such as stainless steel and is vacuum sealed at its periphery to the cylindric l wall portion 12. The member extends from the surface of end plate 14 to adjacent the cover 34.

Tuning is accomplished in a specific embodiment shown by axially moving an electrically conductive member 44 of a suitable material such as copper within the outer cavity resonator 30. In the present invention, the conductive member 44 is an annular member which has a substantially U-shaped cross section and is located between the outer wall 15 and the inner anode wall 22. This member 44 provides the other wall of the cavity resonator 30. The tuning member 44 is actuated by means of two rod members 64 which extend through suitable apertures 66 within the end cover 34. The rods 64 have one end secured to the annular member 44 and the other end secured to a cross-bar member 62. An upper pole piece 50 is provided with an extended upper portion 68 which extends through an aperture 70 centrally located within the crossbar member 62 and into a centrally extending bore 72 within an actuating rod 60. The rod 60 is attached to the cross-bar member 62 and is slidably mounted within a sleeve member 58. The sleeve member 58 is secured to a magnetic spacer 52. The rod 60 may move within the sleeve member 58 and provide movement of the annular member 44. The tuning member 44 may be moved axially with regard to the magnetron and thereby provide tuning of the magnetron by modifying the dimensions of the outer cavity resonator 30.

The magnetic circuit of the device illustrated in FIG. 2 includes two substantially identical horseshoe magnets 46, a bottom pole piece 48 and the upper pole piece 50. Also included in the magnetic circuit is the magnetic spacer 52 which is a substantially U-shaped member and which serves to connect the upper poles of the magnets 46 to the upper pole piece 50. The magnetic spacer 52 also serves as a support means for the tuning drive mechanism. The pole pieces 48 and 50 and the spacer 52 may be of the suitable magnetic material such as soft iron.

It is therefore seen that this is a substantial conventional tunable coaxial magnetron with the addition of temperature compensation in accordance with the teaching of this invention. The operation of the magnetron and tuning mechanism is fully described in the above-mentioned patents. The operation of the temperature compensating mechanism is as follows: In the steady state tempertaure operation, the outside diameter of the cavity 30 defined by the cylinder 15 is allowed to expand independent of the tube body '10. Since the outside diameter of the resonant cavity 30 is the major frequency determining member, the effective coefiicient of thermal expansion of the tube is reduced due to the low expansion material in the liner 15. The use of conventional means of bimetallic materials to further reduce the coefiicient of thermal expansion is also simplified since a shorter length of bimetallic materials will now suffice. When power is suddenly applied or air cooling is suddenly withdrawn from the device described herein, the path for the heat from the vanes 24 to the radiator 13 heats up rapidly.

But since the major frequency determining member namely 15 is now thermally isolated from the body 10 it will heat up much more slowly. In addition, since the cylinder 15 is of a low expansion material, the total dimensional change will be much smaller than the surrounding copper body which carries the heat. In this manner, this invention provides ample temperature compensation for normal operation of the tube without resorting to the elaborate compensation cavities and elaborate automatic frequency cont-r01 loops.

While there have been shown and described what are at present considered to be the preferred embodiments of the invention, modifications thereto will readily occur to those skilled in the art. It is not desired, therefore, that the invention be limited to the specific arrangement shown and described and it is intended to cover in the appended claims all such modifications.

Iclaim as my invention:

1. A coaxial magnetron comprising a cylindrical cathode, a cylindrical anode surrounding said cathode and coaxial therewith, an outer wall member surrounding said cylindrical anode, a cylindrical liner member positioned on the inner surface of said outer wall member, end plates connecting said outer wall member and said cylindrical anode, said cylindrical liner member defining with said cylindrical anode and said end plates an output cavity resonator; said cylindrical anode, said end plates and outer wall member being of a first material of a predetermined coefficient of thermal expansion and said liner member being of a second material of a lower coefficient of thermal expansion than said first material, said liner member spaced from said outer wall member by low thermal conductivity means.

2. A coaxial magnetron comprising a cylindrical cathode, a cylindrical anode surrounding said cathode and coaxial therewith, an outer wall member surrounding said cylindrical anode, end plates connecting said outer wall member and said cylindrical anode, a liner member positioned on the inner surface of said outer wall member and defining with said cylindrical anode and said end plates an output cavity resonator; said cylindrical anode, said end plates and outer wall member being of a first material of a predetermined coefficient of thermal expansion and high thermal conductivity and said liner member being of a second material of lower coefficient of thermal expansion than said first material and thermal insulating means supporting said liner member from said outer wall member.

3. A coaxial magnetron comprising a cylindrical cathode, a cylindrical anode surrounding said cathode and coaxial therewith, a plurality of anode vanes positioned on the inner wall of said cylindrical anode and extending inwardly towards said cathode and defining anode cavity resonators, an outer cavity resonator surrounding said cylindrical anode wall, said outer cavity resonator annular in shape in which the inner wall is defined by said cylindrical anode and the outer cavity resonator wall defined by a member including a material having a lower coefficient of thermal expansion than the material of said anode wall, said outer cavity resonator including a lower end plate of high thermal conductivity material and secured to an outer cylindrical member surrounding said outer cavity resonator wall, said outer cylindrical wall of a high thermal conductivity material with heat radiating fins provided on the outer surface thereof, said outer cavity resonator wall thermally insulated from said outer cylindrical wall.

4. A coaxial magnetron comprising a cylindrical cathode, a cylindrical anode surrounding said cathode and coaxial therewith, a plurality of anode vanes positioned on the inner wall of said cylindrical anode and extending inwardly towards said cathode and defining anode cavity resonators, an outer cavity resonator surrounding said cylindrical anode wall, said outer cavity resonator annular in shape in which the inner wall is defined by said cylindrical anode and the outer cavity resonator wall is defined by a member of a material having a lower coefiicient of thermal expansion than the material of said anode wall, said outer cavity resonator wall thermally insulated from said anode Wall and means for conducting heat from said anode wall secured to said anode wall and extening beyond said outer cavity resonator wall.

5. A coaxial magnetron comprising a cathode, a cylindrical anode of copper surrounding said cathode and provided with a plurality of anode vanes of copper extending inwardly from said cylindrical anode wall to provide an inner resonant system, an output cavity resonator surrounding said cylindrical anode wall and communicating with said inner resonant system through coupling slots provided in said cylindrical anode wall, said outer cavity resonator defined by said cylindrical anode wall and an outer resonant cavity cylindrical wall surrounding said anode cylindrical wall, said outer cavity resonator of a materialhaving a lower coefiicient of thermal expansion than copper and provided with an electrically conductive coating on the inner surface, an upper and lower end plate of copper provided for defining the outer cavity resonator with said cylindrical anode wall and said outer cavity resonator wall, one of said end plates secured to the said anode cylindrical wall and to an outer member of good thermal conductivity material which surrounds said outer cavity resonator wall, said outer wall having a plurality of heat radiating fins provided on the outer surface thereof and said outer cavity resonator wall spaced from said outer wall and said end covers by low thermally conductive means.

6. A coaxial magnetron comprising a cathode, cylindrical anode surrounding said cathode and provided with a plurality of anode vanes extending inwardly from said cylindrical anode wall to provide an inner resonant system, an output cavity resonator surrounding said cylindrical anode wall and communicating with said inner resonant system through coupling slots provided in said cylindrical anode wall, said outer coaxial resonator defined by said cylindrical anode wall and an outer resonant cavity wall surrounding said anode cylindrical wall, said outer resonant cavity wall of a material having .a lower coefficient of thermal expansion than said anode wall and having an electrically conductive coating on the inner surface, an upper and lower end plate provided for defining the outer cavity resonator with said cylindrical anode wall and said outer cavity resonator wall, one of said end plates secured to the said anode cylindrical wall and to a heat radiating member of good thermal conductivity material, said heat radiating member surrounding said cavity resonator and said outer cavity resonator wall spaced from the outer walls of said cavity resonator.

References Cited UNITED STATES PATENTS 2,852,720 9/1958 Crapuchettes 315-39.75 2,996,690 8/1961 St. Clair 333-83 3,034,014 5/1962 DreXler 3l539.77 3,034,078 5/ 1962 McCoubrey 33383 3,063,030 11/1962 Manzahan et al. 333-83 3,169,211 2/1965 DreXler et a1 315-39.77 3,263,118 7/1966 'Peasley et al. BIS-39.61 X

HERMAN KARL SAALBACH, Primary Examiner. 'PAUL L. GENSLER, Examiner. 

